I'll give this one a shot. I suspect a lot of the BT genetic techniques amount to splicing and trial and error methods, rather than assembling DNA from scratch and knowing what each 'bit' does. It would be too astronomically complicated to do it that way. The BG seem to have a better grasp on the minutiae of the genetic material, whereas the BT are 'hacks' insofar as they just mess with existing material to try to plumb out how it can be applied and added to other DNA.

It seems to me likely that the Scattering BT came back and gave the BT the genetic material to imprint on their gholas that would counter the HM sexual techniques, but that doesn't mean the BT understood how it worked or even what the techniques were that it would counter. If we think of the genetic material they were given as a sort of plug and play system, they could insert it into their ghola without being able to reverse engineer it or have a clue about the details of its origin. It would be like if I had a child install an anti-virus software on his PC; he wouldn't have a clue how a computer virus works, or even which particular virus the software is protecting against, but after installing it he'd nonetheless have the protection. It's one thing for Waff to be told how proficient the HM's are, and another to learn first-hand exactly how far that really goes and what exactly their ghola was designed to counter.